soot

A randomly formed particulate carbon material and may be coarse, fine and/or colloidal in proportions depending on its origin. Soot consists of variable quantities of carbonaceous and inorganic solids together with absorbed and occluded
tars and resins.

Note:

An unwanted by-product of incomplete combustion or pyrolysis. Soot generated within flames consists essentially of aggregates of spheres of carbon.
Soot found in domestic fireplace chimneys contains few aggregates but may contain
substantial amounts of particulate fragments of coke or char. Soot from diesel engines consists essentially of aggregates together with tars and
resins. For historical reasons, the term soot is sometimes incorrectly used for carbon black. This misleading use should be avoided.

Source:

PAC, 1995, 67, 473(Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)) on page 504